In many systems employing phased array antennas, operation with a low spatial sidelobe antenna pattern is required. By way of example, these systems include radar systems, communication systems and sonar systems. If one or more antenna elements fail to operate, satisfactory operation may still be possible as long as the antenna patterns for each of the individual elements in the array is known with sufficient accuracy. Accurate knowledge of the individual antenna patterns permits a low spatial sidelobe antenna pattern to be computed despite the presence of failed antenna elements. If the array antenna patterns are not accurately known, computation of the low sidelobe antenna patterns cannot be performed and satisfactory operation of the phased array antenna is typically not possible.